Chemical Reactions in Biology
Chapter 6.2
What are chemical reactions?
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Chemical reactions occur when the atoms of a substance
are rearranged to form a new substance.
In other words, the composition of a substance must
change. Not necessarily the appearance of a substance, but
what a substance is made of. Water can change to ice or
steam, but the composition does not change. (H2O)
Clues that a chemical change has taken place are the
production of heat or light, or a formation of a new gas,
liquid, or solid.
Chemical Changes
Chemical Equations
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Chemical equations show what substances are
involved in the reaction.
The starting substances that will be changed in the
reaction are called reactants.
The final substances that were formed by the
reaction are called the products.
CO2 + H2O ---> C6H12O6 + O2
Reactants
Products
Balancing Chemical Equations
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This equation is unbalanced. In other words it has
the proper molecular formulas but not the correct
number of atoms. Can you balance the equation?
CO2 + H2O ---> C6H12O6 + O2
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1 Carbon
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2 Hydrogens
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3 Oxygens
6 Carbons
12 Hydrogens
8 Oxygens
Activation Energy
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Most chemical reactions require an energy source
in order to start the reaction.
The minimum amount of energy that is required to
start a reaction is called the Activation Energy.
A Catalyst is a substance that lowers the activation
energy of a chemical reaction. Another important
property of a catalyst is that it does not get used in
the reaction. That means it is reusable.
Activation Energy with Endothermic and
Exothermic Reactions
Enzymes
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Enzymes are special proteins essential to life that
act as biological catalysts.
They speed up normal body reactions without
being used up in the reaction themselves.
Without enzymes, our bodies would not function.
Normal metabolism requires thousands of complex
chemical reactions.
Without enzymes, these reactions in our bodies
could not take place.
Enzymes and Activation Energy
Examples of Enzymes and their Function
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Amylase – Breaks down starches
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Cellulase – Breaks down fibers
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Lactase – Breaks down dairy products
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Lipase – Breaks down fats
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Maltase – Breaks down grains
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Protease – Breaks down proteins
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Sucrase – Breaks down sugars
How an Enzyme works
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Enzymes can only react with certain reactants.
It kind of works like a puzzle. Specific reactants in
a reaction are called substrates. Substrates have a
specific site that only matches with a specific
enzyme. That site is called the active site.
Once the active site on the substrate matches with
an enzyme, the enzyme causes the substrate to
change shape or form to make new products. Then
the enzyme is released.
Enzymes and Substrates
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Enzymes can be destroyed or affected by certain
factors such as high or low pH and high or low
temperatures. Optimum enzyme activity in humans
is 37 C0 or 98.6 F0.